David Cameron had to rely on an official 'crib sheet' telling him the price of milk to avoid looking out of touch in interviews, it has been claimed.

The Prime Minister was given a sheet listing the prices of common food items, including loaves of bread and mars bars, as well as the average price of a pint in London and Sheffield, according to a new book by former Lib Dem minister David Laws.

Mr Laws claims to have seen the notes in a confidential economics briefing prepared for the PM and Deputy PM Nick Clegg , which was slipped into Mr Clegg's ministerial red box.

In scenes which recalled the 'zeitgeist tape' - which helped BBC Comedy The Thick Of It's fictional prime minister seem 'with it' - the PM's crib sheet also included a run down of the hit pop songs and movies of the day.

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It listed Rita Ora's I Will Never Let You Down, and movies Bad Neighbours and The Amazing Spiderman 2 among the popular movies.

In his book, Coalition, Mr Laws wrote: "Politicians may not always know the top rate of capital gains tax but they don't want to be accused of being 'posh boys who don't know the price of milk."